Lawn Sleeves Meaning

Example: Used other than as an idiom: see lawn,‎ sleeves.
The sleeves of a bishop's ceremonial garments.
1800, The Parliamentary Register, volume 12, page 481, "House of Lords, Wedneday, July 23" 1800
  The LORD CHANCELLOR declared, that in his opinion, a bishop might vote either in his lawn sleeves, or in his robes ; and in proof of it, his Lordship said he hasd more than once seen Bishops vote in a Committee of Privileges without their lawn sleeves.
The bishops of the Anglican or Roman Catholic churches.
1777, “Debate on Lord C------n's motion more amending the address”[1], in John Nichols, editor, The Gentleman's magazine, volume 47, E. Cave, page 606:
  I shall implore the aid of the lawn sleeves and ermine on that occasion.
1845[2], James Anthony Froude, John Tulloch, editor, Fraser's Magazine, volume 32, J. Fraser:
  â€œIn the House of Lords, most likely. I rather think of bein there to-morrow night, and shal look sharpish after the lawn sleeves, you ma depend on’t."